EXCITATION AND IONIZATION DYNAMICS IN SHORT-PULSE MULTIPHOTON IONIZATION

We present results from a time-dependent two-level-plus-continuum mode l of multiphoton ionization in order to better understand the short-pu lse photoelectron spectrum resulting from multiphoton ionization and t he role of intermediate states. Both resonant and nonresonant populati on transfer to the upper state are found to play an important role in the multiphonon ionization process. The dynamic modeling reveals the p otential for broadening and shifting peaks in the photoelectron spectr um. However, we conclude that despite the complex dynamics of the exci tation, short-pulse photoelectron spectra can be used to measure ac St ark shifts of both nonponderomotively and nonponderomotively shifted s tates in strong laser fields.